The present invention relates to a multi-purpose aqueous cooling lubricant suitable for the mechanical working of many different metals and alloys. The cooling lubricant, containing as essential components a phosphate ester compound and a dicarboxylic acid, contributes to excellent corrosion inhibiting and lubrication properties.
The mechanical working of metals is often performed in the presence of an aqueous cooling lubricant. A disadvantage of many aqueous cooling lubricants is that they frequently contain an iron corrosion inhibitor, such as monoethanolamine, diethanolamine or triethanolamine, which has a detrimental effect and causes discoloration and dissolution when used with cobalt, copper, aluminum, lead or zinc or alloys thereof. Besides the corrosion, any dissolved metal may also constitute a human health and environmental hazard and is difficult to remove from water in the process of disposal of the cooling lubricant.
In order to mitigate the negative effects of the alkanol amine, anionic surface active components with long aliphatic groups, such as groups with 14-44 carbon atoms have been added. Exemplary components are phosphate esters, fatty acids and dinner acids. Their protective action depends on the formation of water-insoluable, organic layers on the metal surfaces. If, however, dissolved di- or trivalent metals exist in the cooling lubricant, the aninic components will form water-insoluable salts with these metal ions. This may sometimes further increase the corrosion inhibiting effect, but it will also lead to the formation of an undesirable sticky precipitation, which, e.g., tends to interfere with the purification of the cooling lubricant. Another drawback is the difficulty to remove the hydrophobic layers formed on the metal surfaces. If they are not removed, they could cause problems in the subsequent surface treatments, for example pickling, phosphatizing, galvanizing or other metal depositing processes. The presence of the long chain anionic components may also cause undesirable foaming and scum.
U.S. Pat. No. 4,315,889 discloses a method of reducing the release of cobalt by performing the metal working in the presence of a cooling lubricant containing, as an active component, a specific triazole or thiadiazole compound. However, since these active compounds are consumed in the presence of ethanolamines, the aqueous cooling lubricant has to be regularly upgraded.
EP-A-0180561 describes the use of a tertiary alkanol amine compound for reducing the release of cobalt. According to the application, the tertiary alkanol amine compound can advantageously be combined with carboxylic acids to further increase the protection against the release of cobalt and the corrosion of iron.
DE-OS-2 943 963 discloses the use of an alkanolamine salt of alkenyl succinic acid as a corrosion inhibitor in aqueous solutions and U.S. Pat. No. 4,670,168 describes a metalworking composition containing a water-soluable polyalkylenegylcol and a neutralized or partially neutralized alkenyl succinic acid.